SQL

Query, join, and model data like a pro.

3 articles

A table of sales rows split into two partitions, with a running total calculated down each one

SQLIntermediate

SQL Window Functions: Running Totals, Rankings and Moving Averages

GROUP BY squashes rows together; window functions calculate across rows and keep every one of them. Learn OVER, PARTITION BY, ROW_NUMBER, RANK, LAG and window frames with small, runnable examples.

Oct 29, 20267 min read

A B-tree index narrowing a search from a million rows down to a single leaf page

SQLAdvanced

SQL Indexes and Query Plans: Making Slow Queries Fast

Learn how B-tree indexes really work, read query plans with EXPLAIN, choose the right column order for composite indexes, and spot the mistakes that silently disable an index.

Oct 29, 20268 min read

Venn diagram of a customers table and an orders table overlapping where a join matches rows

SQLBeginner

SQL JOINs Explained with Simple Examples

INNER, LEFT, RIGHT and FULL joins demystified with two tiny tables. See exactly which rows each join returns, and why.

Sep 23, 20264 min read